This invention relates to chain stitch sewing machines of the type having thread carrying loopers and more particularly for mechanism to throw the looper away from its normal operating position so as to be readily available for convenient threading.
In some chain stitch sewing machines, a looper usually with an eye near its point is designed to carry a lower thread through the loop of the needle thread which is formed beneath the fabric. This action of the looper enables the needle thread loop to enclose a lower thread in the formation of the chain stitch. Because of the action of the looper relative to the needle, and the normal operative position of the looper, it is extremely difficult to thread the looper unless it is moved to a retracted position.
Mechanisms for retracting the looper to threading position by bodily moving the looper carrier as distinguished from a mere pivotable movement of the looper carriers, are known in the prior art. Also known in the prior art for accomplishing this, is mechanism consisting of an eccentric bushing supporting the stud shaft of the looper carrier so that when the bushing is turned, the looper carrier and looper are bodily moved out of the normal operating position into a convenient threading position. Examples of this construction are illustrated in U.S. Pat. Nos. 1,915,923 and 2,397,336.
With the higher speeds attainable by present day sewing machines, it has been found necessary to securely lock the bushing relatively to the frame so as to prevent undesirable movement of the looper from its normal operating position while the sewing machine is operating. Japanese Utility Model No. 75855/73 illustrates a chain stitch sewing machine having an oscillating looper which moves along the line of feed and includes an eccentric member which can be used for moving the looper out of the normal operating position and into a threading position, and has a knob and a detent pin for locking the loopers in the operating position.